Coulometric titration



Oct. 27, 1964 R. B. KESLER 3,154,477

COULOMETRIC TITRATION Filed June 20, 1962 66 DIRECT g ,10 CURRENT SOURCEZ4 ZZ\\ 1 POTENTIOMETEE 1.54 I 66 RECORDER Z5 CONTROLLER "REAGENT 62PUMP .50 1 34 5g AQUEOUS 36 49 52 NAOH c 4g .40 LIQUOR A22 A .Jfia

iw f i zw qzidd/ A7775 rates The present invention generally relates tocoulometric titrations, and more particularly, it relates to a systemfor continuously titrating a stream of reactants, in which system areagent for the titration is continuously generated by means of animproved external reagent-generating electrolysis cell.

In the pulping industry, as in other industries, it is often importantto be able to determine the concentration of certain constituents insolutions, such as treating liquors and waste liquors resulting from thepulping treatment. In the latter connection, it is desirable tocontinuously monitor the sulfide content of green and white liquors, thetotal S content of sulfite cooking acids, sodium sulfite content ofneutral sulfite cooking liquor, and S0 and ammonia in ammonia basecooking liquors. It is also desirable to determine the concentration ofoxidizable sulfur compounds, including S0 in sulfur burner gas andrecovery boiler stack gases.

Continuous monitoring of a flow stream has certain obvious advantages incontrast to only periodic analysis of flow stream samples. Fluctuationsin reactants concentration in a flow stream can be quickly andaccurately detected and adjustments can be made to permit moresatisfactory use of the flow stream. Whether such a titration is to becarried out on a continuous or periodic basis, it requires an adequatesupply of fresh reagent. Bromine, chlorine and iodine have long beenuseful reagents in titrations, particularly as oxidizing agents incarrying out oxidation-reduction reactions to determine, for example,sulfite content in pulping liquors. These halogens have also been usefulin reacting with various organic compounds by substitution and byaddition. However, standard solutions of these halogens are difiicult tostore due to their volatility, susceptibility to photodecomposition, andfor other reasons. In some instances, it has been necessary to preparestandard solutions of bromate-bromide, iodate-iodide, andchlorate-chloride mixtures, which could then be reacted at the time ofrequired use to produce the desired halogens. However, in suchinstances, it has been necessary to go through tedious standardizationand preparation procedures in order to assure accurate concentrations ofthe desired halogen reagents for use in the titrations, such as pulpingliquor titrations.

One technique which has been employed for generating desired halogenreagents involves electrolysis of solutions of salts of the halogens.This technique has also been employed with the salts of other suitablereagents. Quantitative analytic titrations known as coulometrictitrations can be carried out with this technique, using an aliquot ofthe liquid containing the unknown to be determined, electrodes forcarrying out electrolytic generation of desired halogen reagent, and asolution of the salt of the desired halogen reagent. Passage of a directcurrent between the electrodes results in the generation of the reagentwhich immediately reacts with the unknown. A suitable endpoint detectiontechnique determines when all the unknown has been reacted, upon whichcurrent passage is terminated, and the titration is ended. The totalcurrent used to generate the halogen reagent is a measure of the totalamount of unknown initially in the cell.

Such a technique requires that all of the current used in the titrationresults in the desired electrolytic genera- BJMAT? Patented Get. 27,I964 "ice tion of reagent, i.e., percent current efiiciency. Moreover,difiiculties are frequently encountered due to chemical deterioration ofthe unknown during the electrolytic generation of the reagent or becauseof reaction of the unknown with one or both of the electrodes, oralternatively, because of decomposition of the unknown in theelectrolyte due to some requirement of the electrolyte to be at aparticular pH temperature or the like.

For example, the in situ generation of bromine from its salt byelectrolysis in the coulometric titration of sodium sulfide in theelectrolyte has been found to be impractical, because the extremely acidenvironment necessary for bromine generation at 100 percent currentefficiency brings about decomposition of sodium sulfide. In addition,the sulfide ion reacts with the usual platinum cathode to form freesulfur at the voltages used for bromine generation in the cell. Such aprocedure has been found to be suitable only on a batch basis for thegeneration of only very small amounts of reagent, due to a practicalupper limit of about 200 ma. for 100 percent efficiency in thegeneration current.

More recently, certain of the problems connected with the in situgeneration of reagent, by electrolysis in a solution containing theunknown to be titrated coulometrically, have been overcome by separatingthe electrolytic cell used for reagent generation from the vessel inwhich the titration of the unknown takes place. In other words, anexternal and separated reagent-generating electrolytic cell has beenemployed. Successful forms of such cells have been designed to operateonly on a batch basis. Due to their particular construction, severalserious difiiculties have still been encountered. In this connection,certain reagents, such as iodine, cannot be generated in such systems at100% current efliciency at currents in excess of 250 ma. Moreover, thegeneration reaction cannot be sustained over a substantial period oftime because of collection of hydrogen gas, or other gaseous reactionproducts around one or both of the electrodes, with resultantfluctuations in the electrical resistance of the cell.

Attempts to overcome this difficulty have been largely directed toincreasing the flow of electrolyte through the cell. However, when suchflow is increased to a point which sweeps out the reaction gases, theconcentration of generated reagent per unit volume of treatedelectrolyte drops excessively so that in many instances a sufficientamount of generated reagent is not present per unit volume ofelectrolyte to satisfactorily perform in the desired titration reactionwith the unknown.

Accordingly, it is a main object of this invention to provide animproved coulometric titration system. It is a further object of thisinvention to provide an external reagent-generating electrolysis cellfor coulometric titration which would be capable of continuouslyoperating over a long period of time at substantially 100 percentcurrent efficiency and at a relatively high current. It is still afurther object to provide a system which would consume electrolyte at ahigh efliciency and would provide generated reagent in an out-flowstream rapidly. It is another object to provide a system operable toutilize an electrolyte which would not need to be made up in accuratelypredetermined concentrations in order to function properly incoulometric titrations.

It is a still further object of the present invention to provide such acell which is stable in continuous operation and not subject tosubstantial fluctuations in electrical resistance. It is also an objectof the present invention to provide a system whereby continuousmonitoring of a flow stream for concentration of unknown can be carriedout utilizing reagents continuously enerated in response to fluctuationsin the concentrations of the unknown in the flow stream.

Further objects and advantages of the present invention will be apparentfrom a study of the following detailed description and the accompanyingdrawings of which:

FIGURE 1 is a schematic flow diagram illustrating components in oneembodiment in a continuous monitoring coulometric titration system ofthe present invention;

FIGURE 2 is a side elevation of a preferred embodiment of the externalreagent generating electrolytic cell of the present invention,utilizable in the system set forth in FIGURE 1, portions of said cellbeing broken away to illustrate the internal construction thereof; and,

FIGURE 3 is an enlarged fragmentary cross section of the anode of thecell of FIGURE 2, illustrating the internal construction thereof.

An external reagent-generating electrolytic cell has been discoveredwhich satisfies the indicated needs and which can be operatedcontinuously at high currents and at substantially 100 percent currentefliciency over an extended period of time using an electrolyte whichmay be made up using only approximate concentrations of constituents.The cell is capable of furnishing generated halogen reagent in a veryshort period of time.

The cell has particular application in an automatic monitoring systemfor use in a wide variety of applications, particularly in themonitoring of pulping liquors for oxidizable chemical constituents, suchas sulfur compounds. The cell is capable of generating a variety ofreagents but is particularly suitable in the continuous generation ofhalogens for use in oxidation-reduction titration reactions.

The system in which the cell is particularly suited automaticallycontrols the rate of generation of reagents in response to theconcentration of titratable reactants in a flow stream beingcontinuously monitored. Accordingly, an improved method has been devisedfor continuously monitoring titratable constituents in a flow stream,using an improved monitoring system which includes the improvedelectrolytic reagent-generating cell of the present invention.

The present invention generally comprises a system for continuouslymonitoring a stream of titratable constituents to continuously determinethe concentration of said constituents, and arrangement forautomatically carrying out continuous titration and for automaticallygenerating reagent for such titration in response to fluctuations in theconcentration of the titratable constituents in the stream.

The present invention also comprises an improved externalreagent-generating electrolytic cell capable of continuously furnishingreagent to the indicated system and also capable of being utilized forother coulometric titrations requiring continuous supplies of freshlygenerated reagents.

Now referring more particularly to FIGURE 1 of the accompanyingdrawings, FIGURE 1 is a schematic flow diagram of a system suitable forcontinuous coulometric titration of a stream, for example, kraft typewhite liquor.

As shown in FIGURE 1, an electrolye reservoir 16 is provided, in theform of a vessel 12. The electrolyte is for use in a continuousreagent-generating electrolytic cell 14 interconnected with thereservoir, as shown in FIGURE 1, through conduits 15a and 15b. Runninginto the reservoir are suitable lines 16a and 16b which can continuouslysupply constitutents requisite in the preparation of the electrolyte inthe reservoir 10. The flow rate of electrolyte from the reservoir can beadjusted, as by means of valves 20a and 20b in lines a and 15b.

As shown more particularly in FIGURE 2, the reagentgeneratingelectrolytic cell 14 is of special construction. It basically includes awire cathode 22 disposed within a generally tubular glass container 24.An anode 26 of particular construction is also provided at the bottom ofthe container 24. An electrolyte over-flow line 28 connects to the sideof the container 24 near the top thereof and a reagent outlet line 30connects to the bottom of the container below the anode 26. The anode 26and cathode 22 are electrically connected in the system, as shown inflow diagram of FIGURE 1.

The reagent outlet line 30, disposed adjacent the bottom of theelectrolytic cell 14, may be provided with a valve 32. In any event,line 30 is connected with a fluid proportioning pump 34. The output ofthis pump 34 may be mixed with the output of a second proportioning pump36 or a third proportioning pump 38. The pumps permit admixing thereagent with the flow stream to be tested and other constituents inproportioned amounts. In the case of a reagent such as bromine,dissolved in aqueous electrolyte, and prepared as more particularlydescribed hereinafter, the second proportioning pump 36 in theparticular process illustrated in the flow diagram FIGURE 1 may beconnected, as by a line 40, to a source of basic solution, for example,sodium hydroxide. The proportioning pump 36 output is connected by line42 with a common line 44 to which the third and first proportioningpumps 38 and 34 are also connected. The basic solution neutralizes acidsin a stream of liquor supplied by line 46 to pump 38 and line 48 to thecommon line 44. The liquor and basic solution are intimately mixed incoils 4-9 in line 44. The basic solution, i.e., sodium hydroxide in thedescribed embodiment, also converts bromine to hypobromite. The brominepasses to line 44 through pump 34 and line 50 and is intimately mixedtherewith in a second coil 52. Reaction between the reagent (sodiumhypobromite) and titratable chemicals in the liquor (sulfite compoundsin the pulping liquor, for example) takes place in line 44 and coils 49and 52. The reacted solution then passes into a second electrolytic cell54 containing two spaced electrodes, for example, a saturated calomelelectrode 56 and a platinum electrode 58, within a suitable vessel 60containing an outlet line 62. This cell is called an flow cell and isconstructed to determine whether the oxidation-reduction reactionbetween the sulfides and hypobromite has been completed and whether anyexcess of either eagent or titratables exists.

In the second electrolytic cell or flow cell 54, the potentialdifference between the electrodes is continuously monitored byelectrical interconnection of the electrodes with apotentiometer-recorder-controller means 64 which may be of aconventional design. Means 64 is, in turn, electrically interconnectedwith a power source 66 of direct current and with a precision resistor68. The power source 66 is also connected with the cathode 22 of cell 14and to the anode 26 through resistor 68.

In operating the system all flow rates are kept relatively constant.

As the concentration of titratable chemicals (sulfides) varies in theliquor stream, the rate of reagent being released from the firstelectrolytic cell 14 is continuously and automatically adjusted byvarying the reagent generation rate. Accordingly, an amount of reagentjust suflicient to maintain a zero oxidation-reduction potential in cell54 (by just completely neutralizing all sulfide present in the liquorflow stream) is continuously released to the liquor fiow stream. Thereagent generation rate is varied by controlling the current flow fromsource 66 to the first electrolytic cell 14. This current flow fromsource 66 is automatically adjusted by thepotentiometerrecorder-controller means 64. The current flow from powermeans 66 is recorded by the means 64 and provides a measure of theconcentration of titratable chemicals in the liquor stream beingcontinuously monitored.

Thus, means 64 effects a plurality of functions. In this connection, itautomatically notes imbalances in the potential in the cell 54 andeffects a compensating increase or decrease in the amount of current fedfrom the power source 66 to the cell 14, depending upon the direction ofthe unbalanced signal received from the sensing elements, that is, theelectrodes in the cell 54. It also records variations in the amount ofcurrent fed to the cell 14 as a direct function of the oxidizablematerials in the liquor stream. A measure of the amount of current fedto the cell 14 is obtained by means of the fixed precision resistor 68which measures the voltage drop thereacross, the resistor beinginterconnected with the cell 14 and the controller means 64, aspreviously described.

Accordingly, the described system automatically compensates forfluctuations in the concentration of oxidizable components in the liquorstream being continuously coulometrically titrated, by decreasing orincreasing the amount of current fed to the cell 14 and, accordingly,automatically decreasing or increasing the rate of generation of thebromine or other reagent in the cell 14.

A preferred embodiment of the reagent generating electrolytic cell 14 ofthe present invention is shown in FIGURES 2 and 3 of the accompanyingdrawings. The cell comprises the elongated container 24 which ispreferably cylindrical in cross section and of suitable non-conductingmaterial, such as glass or other ceramic. Preferably, heat resistantPyrex-type glass is utilized. The container 24 has a lower neck portion70 at the lower end of which is located the anode 26 which is disposedtransversely to the axis of the container 24. Electrolyte admissionlines 15a and 15b are provided in the narrowed neck portion 70approximately half way between the anode and the lower end of thecentrally disposed cathode 22. The cathode is in the form of a helicallyor spirally wound wire extending down through a cork 72 or the like atthe upper end of the container 24 and terminating at about the beginningof the narrowed neck portion. Electrical leads 74 are connected throughthe cell wall to the anode (FIGURE 2). Leads 74 may be protected byfused glass insulators 76 around which may be disposed metallicconnector caps 78, as shown in FIGURE 2. The lower end of cell 14 isfurther narrowed into the reagent outlet line 30. The cell is alsofitted with the electrolyte over-flow line 28 disposed in the wall ofthe main portion of the cell and preferably slanted downwardly at anangle of about 45 degrees from the horizontal position.

In order to facilitate the flow of electrolyte through the cell 14 andto prevent accumulation of reaction gases on one or both of theelectrodes, particularly the anode 26 with resultant fluctuations inelectrical resistance in the cell, a bafde 80 is provided between theupper part of the electrolyte inlet lines 15a and 15b and the lower endof the cathode 22. The battle 80 is preferably in the form of anopen-topped frusto-conical structure of glass with the lower wider,peripheral portion thereof connected to the wall of the narrowed neckportion 70 of the cell, as by fusing it thereto.

Now referring more particularly to FIGURE 3 of the accompanyingdrawings, the anode 26 is of specified construction to facilitate rapiduniform electrolysis in the cell 14. The anode 26 extends across thecell and is sealed thereto along its periphery. The anode 26 is formedof a plurality of porous metallic platinum disks fused to one anotherand disposed in stacked relation. Approximately midway in the stack ofdisks there is disposed on two opposite sides of the disks a shortlength of electrical lead wire, preferably platinum wire fused by thetwo adjoining fused disks. The outer end of the platinum wire comprisesleads 74. Preferably, each disk is in the form of platinum wire of about52 mesh, and there are usually about disks in a stack to form an anode.

A preferred method of assembling the anode 26 comprises laying one ofthe disks on top of another so that the two disks are concentric but arerotated 90 degrees in respect of one another. The disks can then beheated,

as by an oxygen gas flame, to about the fusion temperature of platinum,and then can be tapped lightly with a hammer, also heated in the flame,so that the disks fuse at the knuckles of the wire mesh. This procedureis repeated upon the addition of each new disk to the top of the stackof the disks. After about five (5) of the disks have been thusassembled, 20 guage electrical wire, preferably platinum, flattened onone end for approximately 1.2 mm., is disposed at diametrically opposedpoints on the top surface of the uppermost disk, so that about 1 mm.total length of each wire rests on the disk. Each wire is then welded,as by flame welding, to the uppermost disk in the manner previouslydescribed for assembling the disks with each other. Another disk is thendisposed on the top of the partially built structure and is fusedthereto, as previously described, so that it becomes fused to not onlythe next underlying disk but also to the two diametrically opposedwires. Succeeding disks are then fused, as previously described, so thatin the finished assembly all disks are fused to adjacent disks and thewires are disposed about midway in the stack of disks. The two wires areused to achieve a relatively even distribution of current throughout theanode. Thus, a porous anode 26 is obtained.

The following example illustrates various features of the presentinvention.

Example I An anode 26 is made of mm. diameter disk cut from 52 meshplatinum gauze and two 10 mm. lengths of 20 gauze platinum wire, 74,assembled in the previously described manner, with 5 disks fusedtogether below the wires and another 5 disks together above the wiresand the disks adjoining the Wires fused with each other and with thewires. The anode is then fused inside a Pyrex tube of about 10 mm.diameter, holes having been made in the appropriate locations in thetube walls through which the two lead wires 74 from the anode 26 extendoutwardly. Small nipples of Pyrex are then fused around the protrudinglead wires and on the exterior of the Pyrex tube metal connector caps 78are placed over the nipples and the lead wires and then soldered to thecaps. The caps are then securely fastened to the outer wall of the 12mm. diameter tube with Apiezon W-lOO Sealing Wax. The anode isdimensioned to fit tightly inside the Pyrex container 24 and is fusedthereto so that no space exists between the perimeter of the anode andthe inner wall of the tube.

The 12 mm. diameter tube is then sharply tapered to 4 mm. diameterimmediately beneath the anode 26 and is fused to an 8 mm. length of 4mm. outside diameter Pyrex tubing 30. About 4 mm. above the uppersurface of the anode, two 8 mm. lengths of 4 mm. outside diameter Pyrextubing 15a and 15b are fused through the wall of the container atdiametrically opposite positions, as illustrated in FIGURE 2 of theaccompanying drawings. These tubes 15a and 15b are utilized to conductelectrolyte continuously into the cell.

Immediately above these two tubes a baflle is fused into place, as shownin FIGURE 2 and comprises an inverted truncated cone-shaped glass memberhaving an fis-inch diameter orifice at the top. The baflie channelsreaction gases out of proximity to the anode 26. Immediately above thepoint of fusion of the baflle with the cell wall, the 12 mm. tubingsection expands to a 22 mm. outside diameter Pyrex tube. The 22 mm. tubesection is 8 cm. long. About 4.5 cm. below the upper end of the 22 mm.tube, a 2 cm. length of 10 mm. outside diameter tubing of Pyrex glass isconnected through the wall at the downward angle of about 45 degrees.This tubing serves as the overflow outlet 28 for electrolyte passingupwardly through the cell from the electrolyte inlets.

The cathode 22 comprises a 20 gauge platinum wire about 13 cm. long iswound to a spiral form at the lower end, and is axially centered by the22 mm. tubing 7 section. The cathode is held in the central position bypassing its upper end through a cork or rubber stopper 72 disposed atthe upper end of the container 24. The cathode leads and the anode leadsare connected, as shown in FIGURE 1.

Before the electrolyte cell is put into the operation, it is necessaryto free it of all air bubbles, particularly those adjacent the anode.Thus, the cell can be filled with distilled water, and subjected tovacuum to eliminate gases. After the cell is completely filled, a vacuumline can be connected to the reagent outlet line 28 and rapid openingand closing of the valve to the vacuum line will sweep any remaining airbubbles which may have adhered to the anode 26 out of the cell by meansof the high velocity of the water passing downwardly through the anodeand out the reagent outlet under the action of the vacuum. During thisprocedure, the top of the cell is open and the liquid level ismaintained at about the baflle level. The cell is then ready forcontinuous operation and the water in the cell is gradually displaced byelectrolyte. When the electrolyte feed lines 15a and 15b are connectedto the electrolyte inlet lines of cell 14, air is prevented from passingthrough the feed lines into the cell.

During operation of cell 14, the electrolyte is passed into the cell ata flow rate slightly above the rate of withdrawal of reagent-containingelectrolyte from the bottom of the cell through line 30. The excesselectrolyte flows upwardly through the baffle into the cathode chamberand passes from the cell out the discharge line 28. Reagent is generatedby electrolytic action between the two electrodes, the rate ofgeneration being determined by the rate of current flow to the cell. Ahalogenyielding salt, for example, in the electrolyte is decomposed toyield the corresponding halogen, which, in turn, goes into solution inthe liquid electrolyte and is withdrawn from the cell through the outletline 30.

Example H further illustrates certain features of the present invention.

Example II An aqueous solution containing 1.5 gram moles per liter ofsulfuric acid and 0.30 gram mole per liter of potassium bromide was fedto the reagent-generating cell 14 shown in FIGURE 1, from the reservoir10 at a rate of 6.3 ml. per minute and reagent-containing liquid wasdrawn off from the cell at a rate of 3.4 ml. per minute. Accordingly,2.9 ml. per minute of electrolyte flowed upwardly into the cathodechamber and exited the reagent generating cell 14 as substantiallyunreacted electrolyte; and 3.4 ml. of the reacted electrolyte containedgenerated bromine and passed from the generation cell in the previouslyindicated manner.

It was found that direct current could be used at a rate of at least 825ma. at 100 percent efficiency for indefinite periods of time in thecontinuous production of bromine at the anode of the cell according tothe following reaction:

The particular construction of the reagent-generating electrolytic cellof the present invention assures efficient performance. Accumulation ofreaction gases adjacent the anode and cathode is prevented by thepositioning of the bafile 80, by permitting electrolyte flow downthrough the anode, which is disposed transverse of the longitudinal axisof the cell, and by providing for an overflow of electrolyte from thecell through the over-flow arm above the level of both electrodes. Eachof these means tends to sweep reaction gases out of the cell. All threemeans cooperate to provide improved results in this respect, so thatfluctuations in electrical resistance in the cell are avoided and,accordingly, the cell can be used accurately and continuously. Moreover,the manner of electrical connection with the anode assures a currentdensity distributed uniformly through the anode, improving theelliciency thereof.

It has been found that current rates of up to 825 ma. can besuccessfully sustained for long periods of time with the electrolytecell operating continuously, in contrast to known cells, which permitonly very low current rates usually not in excess of about 200 ma. andwhich do not operate continuously. Such cells, in contrast to thepresent cell, cannot provide a wide range of concentrations of rapidlyformed reagent for use in titrating a liquid stream of constantlyvarying concentrations of titratables.

For the first time, an external reagent-generating electrolytic cell isprovided which can operate successfully and continuously over a Widerange of current rates to provide a wide range of reagent concentrationsat a rapid generation rate. The cell operates with 100 percent currentefiiciency at up to 825 ma. current rate and with uniform electricalresistance during continuous operation. The cell consumes theelectrolyte very efficiently so that a very high electrolyte flow rateis not needed. In the sample cell set forth above, having the indicateddimensions, the electrolyte rate does not exceed about 4.3 ml. perminute, the hold up volume in the cell does not exceed 1 to 1.5 ml. perminute and, accordingly, the generated reagent is available from thecell in about 20 seconds after it is generated.

Iodine has been continuously generated at currents of 525 ma. from aniodide salt containing electrolyte for periods of up to 9 hours withthis cell, and with 100 percent current efficiency. Bromine has beengenerated under the same conditions for 9 hours at 825 ma. The cell isalso adaptable for use in generating chlorine and other reagents. Whenthe reagent-generating cell of the present invention is connected into asystem, such as indicated in FIGURE 1 of the accompanying drawings,titrations can be continuously carried out with high accuracy.

It will be understood that the described system, an embodiment of whichis illustrated in FIGURE 1, and the method of continuous titrationemploying such a system, are successful because of the unique propertiesof the electrolytic cell. Thus, this cell is capable of continuouslyoperating at substantially 100 percent current efficiency over a widerange of current rates for long periods of time without substantialfluctuations in electrical resistance. Moreover, the cell rapidlyresponds to changes in current rates with corresponding changes inreagent concentration per unit volume and is capable of delivering theformed reagent at a rapid rate to the liquor stream.

Various of the features of the present invention are set forth in theappended claims.

What is claimed is:

1. An improved titration reagent generating electrolytic cell comprisinga container having an outlet adjacent the lower end thereof, a porousanode within said container communicating with said outlet, said anodebeing disposed across said outlet and substantially coextensivetherewith, a cathode within said container disposed above said anode andspaced therefrom, an electrolyte inlet into said container intermediatesaid anode and cathode for introducing electrolyte into said containerand an electrolyte overflow outlet in said container above said cathode.

2. An improved titration reagent generating electrolytic cellcomprising, a vertically elongated container disposed in an uprightposition, said container having a neck portion of reduced cross-sectionadjacent the lower end thereof, said neck terminating in an outlet, aporous anode within said neck communicating with said outlet, said anodebeing disposed across said outlet and substantially coextensivetherewith, said anode being formed of a plurality of coextensiveplatinum wire disks fused together, adjacent disks being rotated withrespect to one another, a cathode within said container disposedsubstantially vertically above said anode and spaced therefrom, pluralelectrolyte inlets in opposed sides of said neck intermediate said anodeand cathode for introducing electrolyte into said container, and anelectrolyte overflow outlet in said container above said cathode.

3. An improved titration reagent generating electrolytic cell comprisinga vertically elongated container disposted in an upright position, saidcontainer having a neck portion of reduced cross-section adjacent thelower end thereof, said neck terminating in an outlet, a porous anodewithin said neck communicating with said outlet, said anode beingdisposed across said outlet and substantially coextensive therewith,said anode being formed of a plurality of coextensive platinum wiredisks fused together, adjacent disks being rotated 90 with respect toone another, a cathode within said container disposed substantiallyvertically above said anode and spaced therefrom, plural electrolyteinlets in opposed sides of said neck intermediate said anode and cathodefor introducing electrolyte into said container, baffle means affixed tosaid neck between said electrolyte inlets and said cathode, said bafliemeans including a generally :frusto-conical surface extending into theinterior of the space defined by said neck and terminating adjacent saidcathode, and an electrolyte overflow outlet in said container above saidcathode.

4. An automatic coulometric titration system for continuously monitoringthe composition of a material flow stream comprising, areagent-generating electrolytic cell which includes a container havingan outlet adjacent the lower end thereof, a porous anode within saidcontainer communicating with said outlet, said anode being disposedacross said outlet and substantially coextensive therewith. a cathodewithin said container disposed above said anode and spaced therefrom, anelectrolyte inlet into said container intermediate said anode andcathode for introducing electrolyte into said container, and anelectrolyte overflow outlet in said container above said cathode, saidreagent generating cell being spaced from the stream of material, meansfor introducing reagent into the stream of material, a reference cellfor measuring the voltage potential of the resulting mixture of reagentand material, a direct current source connected to said reagentgenerating cell and means connecting said direct current source and saidreference cell and adapted to record and control the current output fromsaid direct current source to said reagent generating cell in responseto the voltage potential of said reference cell, whereby the rate ofgeneration of the reagent is automatically controlled in response to thecurrent passed to said cell from said current source.

5. An automatic coulometric titration system for continuously monitoringthe composition of a material flow stream comprising, areagent-generating electrolytic cell which includes a verticallyelongated container disposed in an upright position, said containerhaving a neck portion of reduced cross+section adjacent the lower endthereof, said neck terminating in an outlet, a porous anode within saidneck communicating with said outlet, said anode being disposed acrosssaid outlet and substantially coextensive therewith, said anode beingformed of a plurality of coextensive platinum wire disks fused together,adjacent disks being rotated 90 with respect to one another, a cathodewithin said container disposed substantially vertically above said anodeand spaced therefrom, plural electrolyte inlets in opposed sides of saidneck intermediate said anode and cathode for introducing electrolyteinto said container, and an electrolyte overflow onetlet in saidcontainer above said cathode, said reagent generating cell being spacedfrom the stream of material, means for introducing reagent into thestream of material, means for forming a mixture of the reagent and thestream of material, a reference cell for measuring the voltage potentialof the mixture, a direct current source connected to said reagentgenerating cell and means connecting said direct current source and saidreference cell and adapted to record and control the current output fromsaid direct current source to said reagent generating cell in responseto the voltage potential of said reference cell, whereby the rate ofgeneration of the reagent is automatically controlled in response to thecurrent passed to said cell from said current source.

6. A continuous method of monitoring the composition of a material flowstream by coulometric titration techniques, which method comprises thesteps of continuously generating a titration reagent in an externalelectrolytic cell by continuously passing electrolyte into a zonebetween an anode and a cathode of the cell, positioning the anode belowthe cathode, withdrawing reagent from below the anode, controllingintroduction of electrolyte of reagent from the cell so that an excessof electrolyte enters the cell, withdrawing excess electrolyte from thecell above the level of the electrodes, mixing the reagent with amaterial flow stream, measuring the electrical potential of theresulting mixture, and controlling the current flow to the cell inresponse to such electrical potential.

7. A continuous method of monitoring the composition of a pulpingliquor, which method comprises the steps of continuously generating ahalogen reagent in an external electrolytic cell by continuously passingelectrolyte in a zone between an anode and a cathode of the cell fromopposed sides thereof, positioning the anode below the cathode,withdrawing reagent from below the anode, controlling introduction ofelectrolyte into the cell and withdrawal of halogen reagent from thecell so that an excess of electrolyte enters the cell, withdrawingexcess electrolyte from the cell above the level of the electrodes,forming a mixture of the reagent, an alkali and the material flow streamto be monitored, measuring the electrical potential of the mixture, andcontrolling the current flow to the cell in response to such electricalpotential.

References Cited in the file of this patent UNITED STATES PATENTS813,105 McCarty Feb. 20, 1906 1581,944 Hausmeister Apr. 20, 19262,621,671 Eckfeldt Dec. 16, 1952 2,624,701 Austin Jan. 6, 1953 2,744,061De Ford et a1. May 1, 1956 2,758,079 Eckfeldt Aug. 7, 1956 2,992,170Robinson July 11, 1961 3,051,631 Harbin et a1 Aug. 28, 1962

1. AN IMPROVED TITRATION REAGENT GENERATING ELECTROLYTIC CELL COMPRISINGA CONTAINER HAVING AN OUTLET ADJACENT THE LOWER END THEREOF, A POROUSANODE WITHIN SAID CONTAINER COMMUNICATING WITH SAID OUTLET, SAID ANODEBEING DISPOSED ACROSS SAID OUTLET AND SUBSTANTIALLY COEXTENSIVETHEREWITH, A CATHODE WITHIN SAID CONTAINER DISPOSED ABOVE SAID ANODE ANDSPACED THEREFROM, AN ELECTROLYTE INLET INTO SAID CONTAINER INTERMEDIATESAID ANODE AND CATHODE FOR INTRODUCING ELECTROLYTE INTO SAID CONTAINERAND AN ELECTROLYTE OVERFLOW OUTLET IN SAID CONTAINER ABOVE SAID CATHODE.